Figure 1. Map depicting the site (star) where
Rhadinaea eduardoi
was found.

Table 1. Distinguishing features of three species groups of
Rhadinaea
represented in Mexico (based on data in
Myers 1974
), compared to a new species group erected for the new species described herein.

Rhadinaea
species groups in Mexico

decorata

flavilata

taeniata

eduardoi

Diagnosis.
A snake of the genus
Rhadinaea
that can be distinguished from all congeners by the following combination of morphological features: supralabials 7, with 3rd and 4th entering orbit; 120 ventrals; 71 subcaudals; one subpreocular (lower preocular); 17 dorsal scales throughout body; a head pattern lacking postorbital pale markings but having a pale line extending from the lower rear quadrant of the eye to the ultimate supralabial and slightly beyond, and a midbody dorsal color pattern of a lateral series of black dots in the lower apex of the scales of row V and a middorsal line confined to the middorsal scale row consisting of a series of disjunct spots on the posterior apex of otherwise dark brown scales.
Description of holotype
(Figs 2-4). Subadult male, as evidenced by size of the body and partially everted hemipenes; SVL 196 mm; TL 90 mm; TOL 286 mm, TL 31.5% of TOL; head slightly wider than body; HL 8.29 mm; HW 5.73 mm; ED 1.79 mm, about 21.6% of HL; rostral 1.86 mm long and 0.92 mm wide; internasal on right 1.15 mm long and 1.04 mm wide, on left 1.04
x
0.88, contacting anterior and posterior nasals, rostral, and one/both prefrontals; one large preocular subtended by a small subpreocular (lower preocular); two subequal postoculars; temporals 1 + 2, separating supralabials vi and vii from parietals; 7 supralabials, 1st in contact with rostral, anterior and posterior nasals, and 2nd supralabial, 2nd in contact with posterior nasal (narrowly), 1st supralabial, loreal, 3rd supralabial, 3rd in contact with loreal (narrowly), subpreocular, orbit, and 4th supralabial, 4th in contact with 3rd supralabial, orbit, lower postocular, and 5th supralabial, 5th supralabial in contact with 4th supralabial, lower postocular, and 6th supralabial; 6th supralabial in contact with 5th supralabial, lower postocular (narrowly), anterior temporal, lower posterior temporal, and 7th supralabial, 7th supralabial in contact with 6th supralabial, lower posterior temporal, and two posttemporal scales; 8/9 infralabials, 1st pair in medial contact, four in contact with anterior chinshields, 5th the largest; mental 1.29 mm long and 0.90 mm wide, separated from anterior chinshields by medial contact of 1st pair of infralabials; anterior and posterior chinshields more or less subequal in size; four preventrals between posterior chinshields and 1st ventral; smooth dorsal scales arranged in 17 longitudinal rows throughout the body, with no apical pits; 120 ventrals, cloacal scute divided; and 71 paired subcaudals between cloacal scute and terminal spine.

Figure 2. Head and anterior portion of body of holotype of
Rhadinaea eduardoi
.

Coloration
in life of holotype
(Figs 2, 3a, b). The dorsum and lateral portion of the head above the pale lip line is Cinnamon-Rufous (color 31). A white line begins posterior to the posteroventral quadrant of the eye and extends posteriorly to disappear on the neck. A white dash outlined above by black is present on the side of the neck about three scales posterior to the parietal scales and is separated from the pale line on the body. The region of the dorsum of the body above scale row five is Hazel (color 26). A disjunct black stripe is present on the middorsal scale row, consisting of a series of black dots, each of which markings occupies the posterior portion of each dorsal
scale
. The middorsal and lateral portions of the color pattern are separated by a narrow Pale Buff (color 1) line on scale row five that is bordered below by a black spot on the ventral apex of each scale. The lateral region of the dorsum is Cinnamon-Rufous (color 31) that becomes pale and flecked. The chin and anterior portion of the venter is dark gray flecked with black, grading to cream for the remainder of the venter. The lateral portion of each ventral on the anterior portion of the body bears a black spot.

Figure 3. Holotype of
Rhadinaea eduardoi
in life.

Coloration in preservative
(Fig. 4). The dorsum of the head is dark brown. The lateral portion of the snout is very dark brown. The postocular and temporal region of the head is dark brown. The first four supralabials are dark gray, heavily mottled with very dark brown. The pale line on the upper portion of the postocular supralabials is white, bounded above by a black border and below by a broken black mottled border. A pair of longitudinally-arranged white spots bordered above by a black border are located just posterior to the temporal scales on the right side. These posttemporal spots are in line with a black-bordered white stripe and separated from this
stripe's
point of origin by a single dorsal scale. The white supralabial stripe gradually disappears posterior to the head. The underside of the head is gray, heavily speckled with small black dots. This coloration continues onto the anterior portion of the venter, with the speckling decreasing in intensity. A black spot is present at the lateral apex of the ventral scales on the anterior venter. The dark speckling and spotting fades between ventrals, with the remainder of the venter and the ventral portion of the tail a pale yellow. The middorsal region of the body is dark brown. The middorsal row consists of a series of black dots positioned on the posterior apex of each middorsal scale. The dark brown scales of the middorsal and lateral regions of the body are separated by a pale line on the dorsal portion of scale row iv underlain by a black line on the ventral portion of the same scale row.

Etymology.
This species is named in honor of Eduardo Mata-Silva, collector of the holotype. Eduardo is the younger brother of the senior author of this paper, is a resident of
Rio
Grande, Oaxaca, and is a highly valued member of our field crew working in Oaxaca. He also outshines the rest of the crew when it comes to finding snakes, as evidenced by his discovery of the holotype of the snake described herein.
Habitat and natural history observations.Rhadinaea eduardoi
is resident in an area of converted Premontane Wet Forest, which presently supports a plantation of
shade-grown
coffee (Fig. 5). The holotype was found active at 1800 hrs on leaf litter approximately 10 m from a stream after a very light rain. Other herpetofaunal species encountered at this site were the anurans
Craugastor pygmaeus
,
Ptychohyla leonhardschultzei
, and
Exerodonta sumichrasti
, and the lizards
Norops
sp. and
Holcosus undulatus
.

Figure 5. Habitat where holotype of
Rhadinaea eduardoi
was found.

Distribution.This species is known only from the type locality in the Sierra Madre del Sur of southern Oaxaca, Mexico (Fig. 1).Conservation status.Rhadinaea eduardoi
joins the extensive cadre of conservation category priority one species in Mexico designated by
Johnson et al. (2017)
. This species is placed in this category due to its high EVS value and its restriction to a single physiographic region in Mexico. Its EVS can be calculated as 6 + 8 + 2 = 16, placing it in the middle of the high vulnerability category. This score is based on a contributory score of 6 for geographic distribution, because it is known only from the type locality, 8 for ecological distribution, because it is known only from a single forest formation, and 2 for human persecution, because it is semifossorial, non-venomous, and generally escapes human notice. It is restricted furthermore to the Sierra Madre del Sur. The EVS of 16 for this species matches that for
Rhadinaea bogertorum
(
Johnson et al. 2017
), another species of
Rhadinaea
endemic to the state of Oaxaca (
Mata-Silva et al. 2015
). Using reasoning similar to that employed by
Batista et al. (2016)
, we opine that
Rhadinaea eduardoi
can be placed in the Critically Endangered category, according to IUCN criteria B1ab(iii)+2ab(iii).